The main objective of the project is to study the effects of selected abused drugs (cocaine, methylphenidate, secobarbital, methadone, diazepam and marijuana) on individual behaviors in a group of monkeys (stumptail macaques, Macaca arctoides) free-ranging in a large enclosure, and to determine how the effects of each drug depend on such factors as the dominance rank of the subject, the type of behavior, the context in which the behavior occurs, and the baseline rate of the behavior. The research will characterize and quantify the effects of drugs on readily identifiable behaviors normally exhibited by members of a captive group of nonhuman primates. Drugs will be administered acutely alone and in combination to individual adult male monkeys occupying different positions in the dominance hierarchy of the group. Each monkey will be trained to accept intramuscular injections voluntarily and without the use of restraint procedures that would create a stressful environment within the group. The behavior of the treated monkey and its interactions with other monkeys will be recorded on a portable electronic data-acquisition device and subsequently stored in a laboratory computer. The data will be processed and analyzed for changes in seven molar classes of behavior (e.g., aggression, submission, general social activities, affiliation, play, sexual, and self-directed or solitary behavior) to yield dose-effect functions and time-course functions for each class of behavior. Studying the behavior of group-living nonhuman primates to determine the effects of drugs that act on the central nervous system and are abused by humans is especially appropriate and relevant because of the parallels between human and nonhuman primates with respect to many types of behaviors and behavioral interactions. The research will further develop and validate an animal model that can be used to determine the generality of the behavioral effects of drugs observed in individual animal preparations to behavior occurring in groups.